1. Field of the Invention
The present invention generally relates to optical network communication devices, and more particularly to an improved optical multiplexing network having the ability to rearrange signals carried on different optical fibers and add and drop optical signals from these fiber paths.
2. Discussion of the Related Art
Switching systems are well known in the communications field. In the telecommunications field, for example, switching systems are used to route calls from point to point. In this regard, switching systems may be embodied in a central office (CO) or an exchange, and such switching systems often are utilized for routing signals. Thus, the signal from a caller at a first endpoint passes through a local exchange (central office) and perhaps several other intermediate exchanges, in route to the destination or called endpoint.
To achieve its broad functionality, a switching system is generally characterized by a plurality of input lines and a plurality of output lines for carrying information signals. Traditionally, switching systems have been embodied as electrical switching systems. Electric conductor lines carry electrical information signals into and out of the switching system. In manners that are well known in the art, the various electrical signals are multiplexed, modulated, or otherwise manipulated within the switching system so that incoming electrical signals (on incoming lines) may be controllably routed to outgoing signal lines. Electrical switching systems realize certain advantages, which include ease of implementation and flexibility.
As is known, a plurality of electrical information signals may be carried on each incoming signal line. It is relatively easy, in the electrical domain, to separate these signals at a switching system and recombine them in different ways for transmission on the outgoing lines, through modulation or multiplexing techniques that are well known. Of course, the number of electrical signals that may be multiplexed or modulated on any given electric signal line is determined by the bandwidth of the line and the information rate of the electrical signals carried on the line. In this regard, the shortcoming generally recognized in connection with electric switching systems relates to the relatively limited bandwidth of the transmission lines.
In recent years, the proliferation of data communications has placed a significantly increased demand on transmission bandwidths. The information rate (bandwidth) for voice communications is relatively low (typically 64 kbits per second). However, the recent and ever-increasing use of the Internet, and other systems that transmit relatively large amounts of data across communication links, has underscored the bottleneck in electric transmission systems. As a result, optical transmission systems are rapidly replacing electrical transmission systems.
As is known, optical systems have a much larger bandwidth, and with it the ability to transmit a much greater volume of data through a single transmission line. Unfortunately, optical signals and thus optical systems do not have the flexibility that electrical signals have in regard to their ability to multiplex with other optical signals. More specifically, even in optical transmission systems, information signals are generally converted from the optical domain to the electrical domain at the input side of the switching systems, so that signals may be separated and recombined as desired, then electrical signals are converted back to the optical domain on the outgoing side of the switching system. This multiplexing and demultiplexing has been performed traditionally using in the electrical domain, using electrical components.
Recently, however, certain optical devices have been developed, which allow certain limited multiplexing capability in the optical domain. For example, wavelength-division multiplexing (WDM) technology offers a practical solution of multiplexing many high-speed channels at different optical carrier frequencies and transmitting them over a common fiber. As is known, WDM is conceptually similar to frequency division multiplexing in the electrical domain, except that a plurality of optical signals (of differing wavelength) are communicated through a common optical fiber. A significant limitation, however, to these systems is observed at an exchange, wherein certain signals from incoming optical trunks are routed, or switched, to output trunks. Specifically, two different optical signals of similar wavelength cannot be placed on a common optical fiber. As a result, signal wavelength acts as a limitation to the manner and flexibility in which optical signals may be handled at an exchange.
Accordingly, there is an identifiable need to provide an optical switching system that has an improved capability to multiplex and route optical signals in an optical switching system.